The present invention generally relates to network interfacing and, more particularly, to a system for controlling transmission of data between the network stations connected to a network medium and a device and method for adjusting input gain.
There is an ever present demand for transmission of various types of data between computers. A predominate method of transmitting such data includes coding the data into a low frequency base data signal and modulating the base data signal onto a high frequency carrier signal. The high frequency carrier signal is then transmitted across a network cable medium, via RF signal, modulated illumination, or other network medium, to a remote computing station.
At the remote computing station, the high frequency carrier signal must be received and demodulated to recover the original base data signal. In the absence of any distortion of the carrier signal across the network medium, the received carrier would be identical in phase, amplitude, and frequency to the transmitted carrier and could be demodulated using known mixing techniques to recover the base data signal. The base data signal could then be recovered into digital data using known sampling algorithms.
However, the network topology tends to distort the high frequency carrier signal due to numerous branch connections and different lengths of such branches causing numerous reflections of the transmitted carrier. The high frequency carrier is further distorted by spurious noise caused by electrical devices operating in close proximity to the cable medium. Such problems are even more apparent in a network which uses home telephone wiring cables as the network cable medium because the numerous branches and connections are typically designed for transmission of plain old telephone system (POTS) signals in the 0.3 to 3.4 Kilohertz frequency and are not designed for transmission of high frequency carrier signals on the order of 1 Megahertz or higher. The high frequency carrier signals are further distorted by turn-on transients due to on-hook and off-hook noise pulses of the POTS utilizing the network cables.
Such distortion of frequency, amplitude, and phase of the high frequency carrier signal degrades network performance and tends to impede the design of higher rate networks and challenges designers to continually improve modulation techniques and data recovery techniques to improve data rates. For example, under the home phoneline networking alliance (HPNA) 1.0 standard, a 1 Mbit data rate is achieved using pulse position modulation (PPM) of a carrier, while the more recent HPNA 2.0 standard achieves a 10 Mbit data rate using a complex modulation scheme using a frequency diverse quadrature amplitude modulation (QAM). A problem exits in that a PPM modulated carrier signal and a QAM modulated carrier signal have significantly different power envelopes.
Another problem associated with advancing standards and increasing data rates is that, as in the HPNA example, original base data signal amplitude variations and distortions can cause an incoming analog signal to have an amplitude greater than the dynamic range of an analog to digital converter which converts the incoming analog signal into a digital representation of the incoming analog signal. The incoming analog signal can also have an amplitude which is less than the full dynamic range of the analog to digital converter, resulting in the failure to take advantage of the full dynamic range, or resolution, of the analog to digital converter.
Therefore, based on recognized industry goals for size and cost reductions, what is needed is a device and method for adjusting input gain for an amplifier in a receiver capable of receiving distorted, modulated carrier signals potentially using multiple modulation techniques.
The present invention provides a data networking device. The data networking device has a variable gain amplifier having a first selectable impedance and a second selectable impedance for adjusting gain of the variable gain amplifier. The data networking device has an analog to digital converter for converting an analog output signal of the variable gain amplifier to a digital signal. The data networking device has a digital signal monitoring circuit for monitoring the digital signal and supplying feedback signals to actuate the first and second selectable impedances as a function of the digital signal, thereby adjusting the gain of the variable gain amplifier.
According to another aspect of the invention, a method of controlling a variable gain amplifier is disclosed. An analog output signal of the variable gain amplifier is converted to a digital signal by an analog to digital converter. The method includes determining a portion of dynamic range of the analog to digital converter being used to convert the analog output signal of the variable gain amplifier. The method includes providing a first feedback signal to a first selectable impedance and providing a second feedback signal to a second selectable impedance, the first and second feedback signals adjusting the gain of the variable gain amplifier to increase the dynamic range used by the analog to digital converter.